bpo-33378: Add Korean to the language switcher. (GH-6627)

(cherry picked from commit 57794832)
Co-authored-by: Dong-hee Na <donghee.na92@gmail.com>

Doc/tools/static/switchers.js

@@ -21,6 +21,7 @@
       'en': 'English',
       'fr': 'French',
       'ja': 'Japanese',
+      'ko': 'Korean',
   };
 
   function build_version_select(current_version, current_release) {

Misc/NEWS.d/next/Documentation/2018-04-29-04-02-18.bpo-33378.-anAHN.rst

+Add Korean language switcher for https://docs.python.org/3/